org.ow2.asm/asm/7.3.1 : org/objectweb/asm/Frame.java

Frame
http://asm.ow2.io/: ASM, a very small and fast Java bytecode manipulation framework (OW2)
BSD-3-Clause
Eric Bruneton
Eugene Kuleshov
Remi Forax
// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
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// modification, are permitted provided that the following conditions
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//    notice, this list of conditions and the following disclaimer in the
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//
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package org.objectweb.asm;

The input and output stack map frames of a basic block.
Stack map frames are computed in two steps:

  During the visit of each instruction in MethodWriter, the state of the frame at the end of
      the current basic block is updated by simulating the action of the instruction on the
      previous state of this so called "output frame".
  
After all instructions have been visited, a fix point algorithm is used in MethodWriter to compute the "input frame" of each basic block (i.e. the stack map frame at the beginning of the basic block). See MethodWriter.computeAllFrames. 
Output stack map frames are computed relatively to the input frame of the basic block, which
is not yet known when output frames are computed. It is therefore necessary to be able to
represent abstract types such as "the type at position x in the input frame locals" or "the type
at position x from the top of the input frame stack" or even "the type at position x in the input
frame, with y more (or less) array dimensions". This explains the rather complicated type format
used in this class, explained below.
The local variables and the operand stack of input and output frames contain values called
"abstract types" hereafter. An abstract type is represented with 4 fields named DIM, KIND, FLAGS
and VALUE, packed in a single int value for better performance and memory efficiency:
  =====================================
  |...DIM|KIND|.F|...............VALUE|
  =====================================


  the DIM field, stored in the 6 most significant bits, is a signed number of array dimensions (from -32 to 31, included). It can be retrieved with DIM_MASK and a right shift of DIM_SHIFT. 
the KIND field, stored in 4 bits, indicates the kind of VALUE used. These 4 bits can be retrieved with KIND_MASK and, without any shift, must be equal to CONSTANT_KIND, REFERENCE_KIND, UNINITIALIZED_KIND, LOCAL_KIND or STACK_KIND. 
the FLAGS field, stored in 2 bits, contains up to 2 boolean flags. Currently only one flag is defined, namely TOP_IF_LONG_OR_DOUBLE_FLAG. 
the VALUE field, stored in the remaining 20 bits, contains either
      
        one of the constants ITEM_TOP, ITEM_ASM_BOOLEAN, ITEM_ASM_BYTE, ITEM_ASM_CHAR or ITEM_ASM_SHORT, ITEM_INTEGER, ITEM_FLOAT, ITEM_LONG, ITEM_DOUBLE, ITEM_NULL or ITEM_UNINITIALIZED_THIS, if KIND is equal to CONSTANT_KIND. 
the index of a Symbol.TYPE_TAG Symbol in the type table of a SymbolTable, if KIND is equal to REFERENCE_KIND. 
the index of an Symbol.UNINITIALIZED_TYPE_TAG Symbol in the type table of a SymbolTable, if KIND is equal to UNINITIALIZED_KIND. 
the index of a local variable in the input stack frame, if KIND is equal to LOCAL_KIND. 
a position relatively to the top of the stack of the input stack frame, if KIND is equal to STACK_KIND, 

Output frames can contain abstract types of any kind and with a positive or negative array dimension (and even unassigned types, represented by 0 - which does not correspond to any valid abstract type value). Input frames can only contain CONSTANT_KIND, REFERENCE_KIND or UNINITIALIZED_KIND abstract types of positive or null array dimension. In all cases the type table contains only internal type names (array type descriptors are forbidden - array dimensions must be represented through the DIM field). 
The LONG and DOUBLE types are always represented by using two slots (LONG + TOP or DOUBLE +
TOP), for local variables as well as in the operand stack. This is necessary to be able to
simulate DUPx_y instructions, whose effect would be dependent on the concrete types represented
by the abstract types in the stack (which are not always known).
Author: Eric Bruneton/**
 * The input and output stack map frames of a basic block.
 *
 * <p>Stack map frames are computed in two steps:
 *
 * <ul>
 *   <li>During the visit of each instruction in MethodWriter, the state of the frame at the end of
 *       the current basic block is updated by simulating the action of the instruction on the
 *       previous state of this so called "output frame".
 *   <li>After all instructions have been visited, a fix point algorithm is used in MethodWriter to
 *       compute the "input frame" of each basic block (i.e. the stack map frame at the beginning of
 *       the basic block). See {@link MethodWriter#computeAllFrames}.
 * </ul>
 *
 * <p>Output stack map frames are computed relatively to the input frame of the basic block, which
 * is not yet known when output frames are computed. It is therefore necessary to be able to
 * represent abstract types such as "the type at position x in the input frame locals" or "the type
 * at position x from the top of the input frame stack" or even "the type at position x in the input
 * frame, with y more (or less) array dimensions". This explains the rather complicated type format
 * used in this class, explained below.
 *
 * <p>The local variables and the operand stack of input and output frames contain values called
 * "abstract types" hereafter. An abstract type is represented with 4 fields named DIM, KIND, FLAGS
 * and VALUE, packed in a single int value for better performance and memory efficiency:
 *
 * <pre>
 *   =====================================
 *   |...DIM|KIND|.F|...............VALUE|
 *   =====================================
 * </pre>
 *
 * <ul>
 *   <li>the DIM field, stored in the 6 most significant bits, is a signed number of array
 *       dimensions (from -32 to 31, included). It can be retrieved with {@link #DIM_MASK} and a
 *       right shift of {@link #DIM_SHIFT}.
 *   <li>the KIND field, stored in 4 bits, indicates the kind of VALUE used. These 4 bits can be
 *       retrieved with {@link #KIND_MASK} and, without any shift, must be equal to {@link
 *       #CONSTANT_KIND}, {@link #REFERENCE_KIND}, {@link #UNINITIALIZED_KIND}, {@link #LOCAL_KIND}
 *       or {@link #STACK_KIND}.
 *   <li>the FLAGS field, stored in 2 bits, contains up to 2 boolean flags. Currently only one flag
 *       is defined, namely {@link #TOP_IF_LONG_OR_DOUBLE_FLAG}.
 *   <li>the VALUE field, stored in the remaining 20 bits, contains either
 *       <ul>
 *         <li>one of the constants {@link #ITEM_TOP}, {@link #ITEM_ASM_BOOLEAN}, {@link
 *             #ITEM_ASM_BYTE}, {@link #ITEM_ASM_CHAR} or {@link #ITEM_ASM_SHORT}, {@link
 *             #ITEM_INTEGER}, {@link #ITEM_FLOAT}, {@link #ITEM_LONG}, {@link #ITEM_DOUBLE}, {@link
 *             #ITEM_NULL} or {@link #ITEM_UNINITIALIZED_THIS}, if KIND is equal to {@link
 *             #CONSTANT_KIND}.
 *         <li>the index of a {@link Symbol#TYPE_TAG} {@link Symbol} in the type table of a {@link
 *             SymbolTable}, if KIND is equal to {@link #REFERENCE_KIND}.
 *         <li>the index of an {@link Symbol#UNINITIALIZED_TYPE_TAG} {@link Symbol} in the type
 *             table of a SymbolTable, if KIND is equal to {@link #UNINITIALIZED_KIND}.
 *         <li>the index of a local variable in the input stack frame, if KIND is equal to {@link
 *             #LOCAL_KIND}.
 *         <li>a position relatively to the top of the stack of the input stack frame, if KIND is
 *             equal to {@link #STACK_KIND},
 *       </ul>
 * </ul>
 *
 * <p>Output frames can contain abstract types of any kind and with a positive or negative array
 * dimension (and even unassigned types, represented by 0 - which does not correspond to any valid
 * abstract type value). Input frames can only contain CONSTANT_KIND, REFERENCE_KIND or
 * UNINITIALIZED_KIND abstract types of positive or {@literal null} array dimension. In all cases
 * the type table contains only internal type names (array type descriptors are forbidden - array
 * dimensions must be represented through the DIM field).
 *
 * <p>The LONG and DOUBLE types are always represented by using two slots (LONG + TOP or DOUBLE +
 * TOP), for local variables as well as in the operand stack. This is necessary to be able to
 * simulate DUPx_y instructions, whose effect would be dependent on the concrete types represented
 * by the abstract types in the stack (which are not always known).
 *
 * @author Eric Bruneton
 */
class Frame {

  // Constants used in the StackMapTable attribute.
  // See https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.4.

  static final int SAME_FRAME = 0;
  static final int SAME_LOCALS_1_STACK_ITEM_FRAME = 64;
  static final int RESERVED = 128;
  static final int SAME_LOCALS_1_STACK_ITEM_FRAME_EXTENDED = 247;
  static final int CHOP_FRAME = 248;
  static final int SAME_FRAME_EXTENDED = 251;
  static final int APPEND_FRAME = 252;
  static final int FULL_FRAME = 255;

  static final int ITEM_TOP = 0;
  static final int ITEM_INTEGER = 1;
  static final int ITEM_FLOAT = 2;
  static final int ITEM_DOUBLE = 3;
  static final int ITEM_LONG = 4;
  static final int ITEM_NULL = 5;
  static final int ITEM_UNINITIALIZED_THIS = 6;
  static final int ITEM_OBJECT = 7;
  static final int ITEM_UNINITIALIZED = 8;
  // Additional, ASM specific constants used in abstract types below.
  private static final int ITEM_ASM_BOOLEAN = 9;
  private static final int ITEM_ASM_BYTE = 10;
  private static final int ITEM_ASM_CHAR = 11;
  private static final int ITEM_ASM_SHORT = 12;

  // The size and offset in bits of each field of an abstract type.

  private static final int DIM_SIZE = 6;
  private static final int KIND_SIZE = 4;
  private static final int FLAGS_SIZE = 2;
  private static final int VALUE_SIZE = 32 - DIM_SIZE - KIND_SIZE - FLAGS_SIZE;

  private static final int DIM_SHIFT = KIND_SIZE + FLAGS_SIZE + VALUE_SIZE;
  private static final int KIND_SHIFT = FLAGS_SIZE + VALUE_SIZE;
  private static final int FLAGS_SHIFT = VALUE_SIZE;

  // Bitmasks to get each field of an abstract type.

  private static final int DIM_MASK = ((1 << DIM_SIZE) - 1) << DIM_SHIFT;
  private static final int KIND_MASK = ((1 << KIND_SIZE) - 1) << KIND_SHIFT;
  private static final int VALUE_MASK = (1 << VALUE_SIZE) - 1;

  // Constants to manipulate the DIM field of an abstract type.

  The constant to be added to an abstract type to get one with one more array dimension. /** The constant to be added to an abstract type to get one with one more array dimension. */
  private static final int ARRAY_OF = +1 << DIM_SHIFT;

  The constant to be added to an abstract type to get one with one less array dimension. /** The constant to be added to an abstract type to get one with one less array dimension. */
  private static final int ELEMENT_OF = -1 << DIM_SHIFT;

  // Possible values for the KIND field of an abstract type.

  private static final int CONSTANT_KIND = 1 << KIND_SHIFT;
  private static final int REFERENCE_KIND = 2 << KIND_SHIFT;
  private static final int UNINITIALIZED_KIND = 3 << KIND_SHIFT;
  private static final int LOCAL_KIND = 4 << KIND_SHIFT;
  private static final int STACK_KIND = 5 << KIND_SHIFT;

  // Possible flags for the FLAGS field of an abstract type.

  A flag used for LOCAL_KIND and STACK_KIND abstract types, indicating that if the resolved,
concrete type is LONG or DOUBLE, TOP should be used instead (because the value has been
partially overridden with an xSTORE instruction).
/**
   * A flag used for LOCAL_KIND and STACK_KIND abstract types, indicating that if the resolved,
   * concrete type is LONG or DOUBLE, TOP should be used instead (because the value has been
   * partially overridden with an xSTORE instruction).
   */
  private static final int TOP_IF_LONG_OR_DOUBLE_FLAG = 1 << FLAGS_SHIFT;

  // Useful predefined abstract types (all the possible CONSTANT_KIND types).

  private static final int TOP = CONSTANT_KIND | ITEM_TOP;
  private static final int BOOLEAN = CONSTANT_KIND | ITEM_ASM_BOOLEAN;
  private static final int BYTE = CONSTANT_KIND | ITEM_ASM_BYTE;
  private static final int CHAR = CONSTANT_KIND | ITEM_ASM_CHAR;
  private static final int SHORT = CONSTANT_KIND | ITEM_ASM_SHORT;
  private static final int INTEGER = CONSTANT_KIND | ITEM_INTEGER;
  private static final int FLOAT = CONSTANT_KIND | ITEM_FLOAT;
  private static final int LONG = CONSTANT_KIND | ITEM_LONG;
  private static final int DOUBLE = CONSTANT_KIND | ITEM_DOUBLE;
  private static final int NULL = CONSTANT_KIND | ITEM_NULL;
  private static final int UNINITIALIZED_THIS = CONSTANT_KIND | ITEM_UNINITIALIZED_THIS;

  // -----------------------------------------------------------------------------------------------
  // Instance fields
  // -----------------------------------------------------------------------------------------------

  The basic block to which these input and output stack map frames correspond. /** The basic block to which these input and output stack map frames correspond. */
  Label owner;

  The input stack map frame locals. This is an array of abstract types. /** The input stack map frame locals. This is an array of abstract types. */
  private int[] inputLocals;

  The input stack map frame stack. This is an array of abstract types. /** The input stack map frame stack. This is an array of abstract types. */
  private int[] inputStack;

  The output stack map frame locals. This is an array of abstract types. /** The output stack map frame locals. This is an array of abstract types. */
  private int[] outputLocals;

  The output stack map frame stack. This is an array of abstract types. /** The output stack map frame stack. This is an array of abstract types. */
  private int[] outputStack;

  The start of the output stack, relatively to the input stack. This offset is always negative or
null. A null offset means that the output stack must be appended to the input stack. A -n
offset means that the first n output stack elements must replace the top n input stack
elements, and that the other elements must be appended to the input stack.
/**
   * The start of the output stack, relatively to the input stack. This offset is always negative or
   * null. A null offset means that the output stack must be appended to the input stack. A -n
   * offset means that the first n output stack elements must replace the top n input stack
   * elements, and that the other elements must be appended to the input stack.
   */
  private short outputStackStart;

  The index of the top stack element in outputStack. /** The index of the top stack element in {@link #outputStack}. */
  private short outputStackTop;

  The number of types that are initialized in the basic block. See initializations. /** The number of types that are initialized in the basic block. See {@link #initializations}. */
  private int initializationCount;

  The abstract types that are initialized in the basic block. A constructor invocation on an
UNINITIALIZED or UNINITIALIZED_THIS abstract type must replace every occurrence of this
type in the local variables and in the operand stack. This cannot be done during the first step
of the algorithm since, during this step, the local variables and the operand stack types are
still abstract. It is therefore necessary to store the abstract types of the constructors which
are invoked in the basic block, in order to do this replacement during the second step of the
algorithm, where the frames are fully computed. Note that this array can contain abstract types
that are relative to the input locals or to the input stack.
/**
   * The abstract types that are initialized in the basic block. A constructor invocation on an
   * UNINITIALIZED or UNINITIALIZED_THIS abstract type must replace <i>every occurrence</i> of this
   * type in the local variables and in the operand stack. This cannot be done during the first step
   * of the algorithm since, during this step, the local variables and the operand stack types are
   * still abstract. It is therefore necessary to store the abstract types of the constructors which
   * are invoked in the basic block, in order to do this replacement during the second step of the
   * algorithm, where the frames are fully computed. Note that this array can contain abstract types
   * that are relative to the input locals or to the input stack.
   */
  private int[] initializations;

  // -----------------------------------------------------------------------------------------------
  // Constructor
  // -----------------------------------------------------------------------------------------------

  Constructs a new Frame.
Params: owner – the basic block to which these input and output stack map frames correspond./**
   * Constructs a new Frame.
   *
   * @param owner the basic block to which these input and output stack map frames correspond.
   */
  Frame(final Label owner) {
    this.owner = owner;
  }

  Sets this frame to the value of the given frame.
WARNING: after this method is called the two frames share the same data structures. It is
recommended to discard the given frame to avoid unexpected side effects.
Params: frame – The new frame value./**
   * Sets this frame to the value of the given frame.
   *
   * <p>WARNING: after this method is called the two frames share the same data structures. It is
   * recommended to discard the given frame to avoid unexpected side effects.
   *
   * @param frame The new frame value.
   */
  final void copyFrom(final Frame frame) {
    inputLocals = frame.inputLocals;
    inputStack = frame.inputStack;
    outputStackStart = 0;
    outputLocals = frame.outputLocals;
    outputStack = frame.outputStack;
    outputStackTop = frame.outputStackTop;
    initializationCount = frame.initializationCount;
    initializations = frame.initializations;
  }

  // -----------------------------------------------------------------------------------------------
  // Static methods to get abstract types from other type formats
  // -----------------------------------------------------------------------------------------------

  Returns the abstract type corresponding to the given public API frame element type.
Params: symbolTable – the type table to use to lookup and store type Symbol.
type – a frame element type described using the same format as in MethodVisitor.visitFrame, i.e. either Opcodes.TOP, Opcodes.INTEGER, Opcodes.FLOAT, Opcodes.LONG, Opcodes.DOUBLE, Opcodes.NULL, or Opcodes.UNINITIALIZED_THIS, or the internal name of a class, or a Label designating a NEW instruction (for uninitialized types).
Returns: the abstract type corresponding to the given frame element type./**
   * Returns the abstract type corresponding to the given public API frame element type.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param type a frame element type described using the same format as in {@link
   *     MethodVisitor#visitFrame}, i.e. either {@link Opcodes#TOP}, {@link Opcodes#INTEGER}, {@link
   *     Opcodes#FLOAT}, {@link Opcodes#LONG}, {@link Opcodes#DOUBLE}, {@link Opcodes#NULL}, or
   *     {@link Opcodes#UNINITIALIZED_THIS}, or the internal name of a class, or a Label designating
   *     a NEW instruction (for uninitialized types).
   * @return the abstract type corresponding to the given frame element type.
   */
  static int getAbstractTypeFromApiFormat(final SymbolTable symbolTable, final Object type) {
    if (type instanceof Integer) {
      return CONSTANT_KIND | ((Integer) type).intValue();
    } else if (type instanceof String) {
      String descriptor = Type.getObjectType((String) type).getDescriptor();
      return getAbstractTypeFromDescriptor(symbolTable, descriptor, 0);
    } else {
      return UNINITIALIZED_KIND
          | symbolTable.addUninitializedType("", ((Label) type).bytecodeOffset);
    }
  }

  Returns the abstract type corresponding to the internal name of a class.
Params: symbolTable – the type table to use to lookup and store type Symbol.
internalName – the internal name of a class. This must not be an array type
    descriptor.
Returns: the abstract type value corresponding to the given internal name./**
   * Returns the abstract type corresponding to the internal name of a class.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param internalName the internal name of a class. This must <i>not</i> be an array type
   *     descriptor.
   * @return the abstract type value corresponding to the given internal name.
   */
  static int getAbstractTypeFromInternalName(
      final SymbolTable symbolTable, final String internalName) {
    return REFERENCE_KIND | symbolTable.addType(internalName);
  }

  Returns the abstract type corresponding to the given type descriptor.
Params: symbolTable – the type table to use to lookup and store type Symbol.
buffer – a string ending with a type descriptor.
offset – the start offset of the type descriptor in buffer.
Returns: the abstract type corresponding to the given type descriptor./**
   * Returns the abstract type corresponding to the given type descriptor.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param buffer a string ending with a type descriptor.
   * @param offset the start offset of the type descriptor in buffer.
   * @return the abstract type corresponding to the given type descriptor.
   */
  private static int getAbstractTypeFromDescriptor(
      final SymbolTable symbolTable, final String buffer, final int offset) {
    String internalName;
    switch (buffer.charAt(offset)) {
      case 'V':
        return 0;
      case 'Z':
      case 'C':
      case 'B':
      case 'S':
      case 'I':
        return INTEGER;
      case 'F':
        return FLOAT;
      case 'J':
        return LONG;
      case 'D':
        return DOUBLE;
      case 'L':
        internalName = buffer.substring(offset + 1, buffer.length() - 1);
        return REFERENCE_KIND | symbolTable.addType(internalName);
      case '[':
        int elementDescriptorOffset = offset + 1;
        while (buffer.charAt(elementDescriptorOffset) == '[') {
          ++elementDescriptorOffset;
        }
        int typeValue;
        switch (buffer.charAt(elementDescriptorOffset)) {
          case 'Z':
            typeValue = BOOLEAN;
            break;
          case 'C':
            typeValue = CHAR;
            break;
          case 'B':
            typeValue = BYTE;
            break;
          case 'S':
            typeValue = SHORT;
            break;
          case 'I':
            typeValue = INTEGER;
            break;
          case 'F':
            typeValue = FLOAT;
            break;
          case 'J':
            typeValue = LONG;
            break;
          case 'D':
            typeValue = DOUBLE;
            break;
          case 'L':
            internalName = buffer.substring(elementDescriptorOffset + 1, buffer.length() - 1);
            typeValue = REFERENCE_KIND | symbolTable.addType(internalName);
            break;
          default:
            throw new IllegalArgumentException();
        }
        return ((elementDescriptorOffset - offset) << DIM_SHIFT) | typeValue;
      default:
        throw new IllegalArgumentException();
    }
  }

  // -----------------------------------------------------------------------------------------------
  // Methods related to the input frame
  // -----------------------------------------------------------------------------------------------

  Sets the input frame from the given method description. This method is used to initialize the
first frame of a method, which is implicit (i.e. not stored explicitly in the StackMapTable
attribute).
Params: symbolTable – the type table to use to lookup and store type Symbol.
access – the method's access flags.
descriptor – the method descriptor.
maxLocals – the maximum number of local variables of the method./**
   * Sets the input frame from the given method description. This method is used to initialize the
   * first frame of a method, which is implicit (i.e. not stored explicitly in the StackMapTable
   * attribute).
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param access the method's access flags.
   * @param descriptor the method descriptor.
   * @param maxLocals the maximum number of local variables of the method.
   */
  final void setInputFrameFromDescriptor(
      final SymbolTable symbolTable,
      final int access,
      final String descriptor,
      final int maxLocals) {
    inputLocals = new int[maxLocals];
    inputStack = new int[0];
    int inputLocalIndex = 0;
    if ((access & Opcodes.ACC_STATIC) == 0) {
      if ((access & Constants.ACC_CONSTRUCTOR) == 0) {
        inputLocals[inputLocalIndex++] =
            REFERENCE_KIND | symbolTable.addType(symbolTable.getClassName());
      } else {
        inputLocals[inputLocalIndex++] = UNINITIALIZED_THIS;
      }
    }
    for (Type argumentType : Type.getArgumentTypes(descriptor)) {
      int abstractType =
          getAbstractTypeFromDescriptor(symbolTable, argumentType.getDescriptor(), 0);
      inputLocals[inputLocalIndex++] = abstractType;
      if (abstractType == LONG || abstractType == DOUBLE) {
        inputLocals[inputLocalIndex++] = TOP;
      }
    }
    while (inputLocalIndex < maxLocals) {
      inputLocals[inputLocalIndex++] = TOP;
    }
  }

  Sets the input frame from the given public API frame description.
Params: symbolTable – the type table to use to lookup and store type Symbol.
numLocal – the number of local variables.
local – the local variable types, described using the same format as in MethodVisitor.visitFrame.
numStack – the number of operand stack elements.
stack – the operand stack types, described using the same format as in MethodVisitor.visitFrame./**
   * Sets the input frame from the given public API frame description.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param numLocal the number of local variables.
   * @param local the local variable types, described using the same format as in {@link
   *     MethodVisitor#visitFrame}.
   * @param numStack the number of operand stack elements.
   * @param stack the operand stack types, described using the same format as in {@link
   *     MethodVisitor#visitFrame}.
   */
  final void setInputFrameFromApiFormat(
      final SymbolTable symbolTable,
      final int numLocal,
      final Object[] local,
      final int numStack,
      final Object[] stack) {
    int inputLocalIndex = 0;
    for (int i = 0; i < numLocal; ++i) {
      inputLocals[inputLocalIndex++] = getAbstractTypeFromApiFormat(symbolTable, local[i]);
      if (local[i] == Opcodes.LONG || local[i] == Opcodes.DOUBLE) {
        inputLocals[inputLocalIndex++] = TOP;
      }
    }
    while (inputLocalIndex < inputLocals.length) {
      inputLocals[inputLocalIndex++] = TOP;
    }
    int numStackTop = 0;
    for (int i = 0; i < numStack; ++i) {
      if (stack[i] == Opcodes.LONG || stack[i] == Opcodes.DOUBLE) {
        ++numStackTop;
      }
    }
    inputStack = new int[numStack + numStackTop];
    int inputStackIndex = 0;
    for (int i = 0; i < numStack; ++i) {
      inputStack[inputStackIndex++] = getAbstractTypeFromApiFormat(symbolTable, stack[i]);
      if (stack[i] == Opcodes.LONG || stack[i] == Opcodes.DOUBLE) {
        inputStack[inputStackIndex++] = TOP;
      }
    }
    outputStackTop = 0;
    initializationCount = 0;
  }

  final int getInputStackSize() {
    return inputStack.length;
  }

  // -----------------------------------------------------------------------------------------------
  // Methods related to the output frame
  // -----------------------------------------------------------------------------------------------

  Returns the abstract type stored at the given local variable index in the output frame.
Params: localIndex – the index of the local variable whose value must be returned.
Returns: the abstract type stored at the given local variable index in the output frame./**
   * Returns the abstract type stored at the given local variable index in the output frame.
   *
   * @param localIndex the index of the local variable whose value must be returned.
   * @return the abstract type stored at the given local variable index in the output frame.
   */
  private int getLocal(final int localIndex) {
    if (outputLocals == null || localIndex >= outputLocals.length) {
      // If this local has never been assigned in this basic block, it is still equal to its value
      // in the input frame.
      return LOCAL_KIND | localIndex;
    } else {
      int abstractType = outputLocals[localIndex];
      if (abstractType == 0) {
        // If this local has never been assigned in this basic block, so it is still equal to its
        // value in the input frame.
        abstractType = outputLocals[localIndex] = LOCAL_KIND | localIndex;
      }
      return abstractType;
    }
  }

  Replaces the abstract type stored at the given local variable index in the output frame.
Params: localIndex – the index of the output frame local variable that must be set.
abstractType – the value that must be set./**
   * Replaces the abstract type stored at the given local variable index in the output frame.
   *
   * @param localIndex the index of the output frame local variable that must be set.
   * @param abstractType the value that must be set.
   */
  private void setLocal(final int localIndex, final int abstractType) {
    // Create and/or resize the output local variables array if necessary.
    if (outputLocals == null) {
      outputLocals = new int[10];
    }
    int outputLocalsLength = outputLocals.length;
    if (localIndex >= outputLocalsLength) {
      int[] newOutputLocals = new int[Math.max(localIndex + 1, 2 * outputLocalsLength)];
      System.arraycopy(outputLocals, 0, newOutputLocals, 0, outputLocalsLength);
      outputLocals = newOutputLocals;
    }
    // Set the local variable.
    outputLocals[localIndex] = abstractType;
  }

  Pushes the given abstract type on the output frame stack.
Params: abstractType – an abstract type./**
   * Pushes the given abstract type on the output frame stack.
   *
   * @param abstractType an abstract type.
   */
  private void push(final int abstractType) {
    // Create and/or resize the output stack array if necessary.
    if (outputStack == null) {
      outputStack = new int[10];
    }
    int outputStackLength = outputStack.length;
    if (outputStackTop >= outputStackLength) {
      int[] newOutputStack = new int[Math.max(outputStackTop + 1, 2 * outputStackLength)];
      System.arraycopy(outputStack, 0, newOutputStack, 0, outputStackLength);
      outputStack = newOutputStack;
    }
    // Pushes the abstract type on the output stack.
    outputStack[outputStackTop++] = abstractType;
    // Updates the maximum size reached by the output stack, if needed (note that this size is
    // relative to the input stack size, which is not known yet).
    short outputStackSize = (short) (outputStackStart + outputStackTop);
    if (outputStackSize > owner.outputStackMax) {
      owner.outputStackMax = outputStackSize;
    }
  }

  Pushes the abstract type corresponding to the given descriptor on the output frame stack.
Params: symbolTable – the type table to use to lookup and store type Symbol.
descriptor – a type or method descriptor (in which case its return type is pushed)./**
   * Pushes the abstract type corresponding to the given descriptor on the output frame stack.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param descriptor a type or method descriptor (in which case its return type is pushed).
   */
  private void push(final SymbolTable symbolTable, final String descriptor) {
    int typeDescriptorOffset =
        descriptor.charAt(0) == '(' ? Type.getReturnTypeOffset(descriptor) : 0;
    int abstractType = getAbstractTypeFromDescriptor(symbolTable, descriptor, typeDescriptorOffset);
    if (abstractType != 0) {
      push(abstractType);
      if (abstractType == LONG || abstractType == DOUBLE) {
        push(TOP);
      }
    }
  }

  Pops an abstract type from the output frame stack and returns its value.
Returns: the abstract type that has been popped from the output frame stack./**
   * Pops an abstract type from the output frame stack and returns its value.
   *
   * @return the abstract type that has been popped from the output frame stack.
   */
  private int pop() {
    if (outputStackTop > 0) {
      return outputStack[--outputStackTop];
    } else {
      // If the output frame stack is empty, pop from the input stack.
      return STACK_KIND | -(--outputStackStart);
    }
  }

  Pops the given number of abstract types from the output frame stack.
Params: elements – the number of abstract types that must be popped./**
   * Pops the given number of abstract types from the output frame stack.
   *
   * @param elements the number of abstract types that must be popped.
   */
  private void pop(final int elements) {
    if (outputStackTop >= elements) {
      outputStackTop -= elements;
    } else {
      // If the number of elements to be popped is greater than the number of elements in the output
      // stack, clear it, and pop the remaining elements from the input stack.
      outputStackStart -= elements - outputStackTop;
      outputStackTop = 0;
    }
  }

  Pops as many abstract types from the output frame stack as described by the given descriptor.
Params: descriptor – a type or method descriptor (in which case its argument types are popped)./**
   * Pops as many abstract types from the output frame stack as described by the given descriptor.
   *
   * @param descriptor a type or method descriptor (in which case its argument types are popped).
   */
  private void pop(final String descriptor) {
    char firstDescriptorChar = descriptor.charAt(0);
    if (firstDescriptorChar == '(') {
      pop((Type.getArgumentsAndReturnSizes(descriptor) >> 2) - 1);
    } else if (firstDescriptorChar == 'J' || firstDescriptorChar == 'D') {
      pop(2);
    } else {
      pop(1);
    }
  }

  // -----------------------------------------------------------------------------------------------
  // Methods to handle uninitialized types
  // -----------------------------------------------------------------------------------------------

  Adds an abstract type to the list of types on which a constructor is invoked in the basic
block.
Params: abstractType – an abstract type on a which a constructor is invoked./**
   * Adds an abstract type to the list of types on which a constructor is invoked in the basic
   * block.
   *
   * @param abstractType an abstract type on a which a constructor is invoked.
   */
  private void addInitializedType(final int abstractType) {
    // Create and/or resize the initializations array if necessary.
    if (initializations == null) {
      initializations = new int[2];
    }
    int initializationsLength = initializations.length;
    if (initializationCount >= initializationsLength) {
      int[] newInitializations =
          new int[Math.max(initializationCount + 1, 2 * initializationsLength)];
      System.arraycopy(initializations, 0, newInitializations, 0, initializationsLength);
      initializations = newInitializations;
    }
    // Store the abstract type.
    initializations[initializationCount++] = abstractType;
  }

  Returns the "initialized" abstract type corresponding to the given abstract type.
Params: symbolTable – the type table to use to lookup and store type Symbol.
abstractType – an abstract type.
Returns: the REFERENCE_KIND abstract type corresponding to abstractType if it is
    UNINITIALIZED_THIS or an UNINITIALIZED_KIND abstract type for one of the types on which a
    constructor is invoked in the basic block. Otherwise returns abstractType./**
   * Returns the "initialized" abstract type corresponding to the given abstract type.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param abstractType an abstract type.
   * @return the REFERENCE_KIND abstract type corresponding to abstractType if it is
   *     UNINITIALIZED_THIS or an UNINITIALIZED_KIND abstract type for one of the types on which a
   *     constructor is invoked in the basic block. Otherwise returns abstractType.
   */
  private int getInitializedType(final SymbolTable symbolTable, final int abstractType) {
    if (abstractType == UNINITIALIZED_THIS
        || (abstractType & (DIM_MASK | KIND_MASK)) == UNINITIALIZED_KIND) {
      for (int i = 0; i < initializationCount; ++i) {
        int initializedType = initializations[i];
        int dim = initializedType & DIM_MASK;
        int kind = initializedType & KIND_MASK;
        int value = initializedType & VALUE_MASK;
        if (kind == LOCAL_KIND) {
          initializedType = dim + inputLocals[value];
        } else if (kind == STACK_KIND) {
          initializedType = dim + inputStack[inputStack.length - value];
        }
        if (abstractType == initializedType) {
          if (abstractType == UNINITIALIZED_THIS) {
            return REFERENCE_KIND | symbolTable.addType(symbolTable.getClassName());
          } else {
            return REFERENCE_KIND
                | symbolTable.addType(symbolTable.getType(abstractType & VALUE_MASK).value);
          }
        }
      }
    }
    return abstractType;
  }

  // -----------------------------------------------------------------------------------------------
  // Main method, to simulate the execution of each instruction on the output frame
  // -----------------------------------------------------------------------------------------------

  Simulates the action of the given instruction on the output stack frame.
Params: opcode – the opcode of the instruction.
arg – the numeric operand of the instruction, if any.
argSymbol – the Symbol operand of the instruction, if any.
symbolTable – the type table to use to lookup and store type Symbol./**
   * Simulates the action of the given instruction on the output stack frame.
   *
   * @param opcode the opcode of the instruction.
   * @param arg the numeric operand of the instruction, if any.
   * @param argSymbol the Symbol operand of the instruction, if any.
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   */
  void execute(
      final int opcode, final int arg, final Symbol argSymbol, final SymbolTable symbolTable) {
    // Abstract types popped from the stack or read from local variables.
    int abstractType1;
    int abstractType2;
    int abstractType3;
    int abstractType4;
    switch (opcode) {
      case Opcodes.NOP:
      case Opcodes.INEG:
      case Opcodes.LNEG:
      case Opcodes.FNEG:
      case Opcodes.DNEG:
      case Opcodes.I2B:
      case Opcodes.I2C:
      case Opcodes.I2S:
      case Opcodes.GOTO:
      case Opcodes.RETURN:
        break;
      case Opcodes.ACONST_NULL:
        push(NULL);
        break;
      case Opcodes.ICONST_M1:
      case Opcodes.ICONST_0:
      case Opcodes.ICONST_1:
      case Opcodes.ICONST_2:
      case Opcodes.ICONST_3:
      case Opcodes.ICONST_4:
      case Opcodes.ICONST_5:
      case Opcodes.BIPUSH:
      case Opcodes.SIPUSH:
      case Opcodes.ILOAD:
        push(INTEGER);
        break;
      case Opcodes.LCONST_0:
      case Opcodes.LCONST_1:
      case Opcodes.LLOAD:
        push(LONG);
        push(TOP);
        break;
      case Opcodes.FCONST_0:
      case Opcodes.FCONST_1:
      case Opcodes.FCONST_2:
      case Opcodes.FLOAD:
        push(FLOAT);
        break;
      case Opcodes.DCONST_0:
      case Opcodes.DCONST_1:
      case Opcodes.DLOAD:
        push(DOUBLE);
        push(TOP);
        break;
      case Opcodes.LDC:
        switch (argSymbol.tag) {
          case Symbol.CONSTANT_INTEGER_TAG:
            push(INTEGER);
            break;
          case Symbol.CONSTANT_LONG_TAG:
            push(LONG);
            push(TOP);
            break;
          case Symbol.CONSTANT_FLOAT_TAG:
            push(FLOAT);
            break;
          case Symbol.CONSTANT_DOUBLE_TAG:
            push(DOUBLE);
            push(TOP);
            break;
          case Symbol.CONSTANT_CLASS_TAG:
            push(REFERENCE_KIND | symbolTable.addType("java/lang/Class"));
            break;
          case Symbol.CONSTANT_STRING_TAG:
            push(REFERENCE_KIND | symbolTable.addType("java/lang/String"));
            break;
          case Symbol.CONSTANT_METHOD_TYPE_TAG:
            push(REFERENCE_KIND | symbolTable.addType("java/lang/invoke/MethodType"));
            break;
          case Symbol.CONSTANT_METHOD_HANDLE_TAG:
            push(REFERENCE_KIND | symbolTable.addType("java/lang/invoke/MethodHandle"));
            break;
          case Symbol.CONSTANT_DYNAMIC_TAG:
            push(symbolTable, argSymbol.value);
            break;
          default:
            throw new AssertionError();
        }
        break;
      case Opcodes.ALOAD:
        push(getLocal(arg));
        break;
      case Opcodes.LALOAD:
      case Opcodes.D2L:
        pop(2);
        push(LONG);
        push(TOP);
        break;
      case Opcodes.DALOAD:
      case Opcodes.L2D:
        pop(2);
        push(DOUBLE);
        push(TOP);
        break;
      case Opcodes.AALOAD:
        pop(1);
        abstractType1 = pop();
        push(abstractType1 == NULL ? abstractType1 : ELEMENT_OF + abstractType1);
        break;
      case Opcodes.ISTORE:
      case Opcodes.FSTORE:
      case Opcodes.ASTORE:
        abstractType1 = pop();
        setLocal(arg, abstractType1);
        if (arg > 0) {
          int previousLocalType = getLocal(arg - 1);
          if (previousLocalType == LONG || previousLocalType == DOUBLE) {
            setLocal(arg - 1, TOP);
          } else if ((previousLocalType & KIND_MASK) == LOCAL_KIND
              || (previousLocalType & KIND_MASK) == STACK_KIND) {
            // The type of the previous local variable is not known yet, but if it later appears
            // to be LONG or DOUBLE, we should then use TOP instead.
            setLocal(arg - 1, previousLocalType | TOP_IF_LONG_OR_DOUBLE_FLAG);
          }
        }
        break;
      case Opcodes.LSTORE:
      case Opcodes.DSTORE:
        pop(1);
        abstractType1 = pop();
        setLocal(arg, abstractType1);
        setLocal(arg + 1, TOP);
        if (arg > 0) {
          int previousLocalType = getLocal(arg - 1);
          if (previousLocalType == LONG || previousLocalType == DOUBLE) {
            setLocal(arg - 1, TOP);
          } else if ((previousLocalType & KIND_MASK) == LOCAL_KIND
              || (previousLocalType & KIND_MASK) == STACK_KIND) {
            // The type of the previous local variable is not known yet, but if it later appears
            // to be LONG or DOUBLE, we should then use TOP instead.
            setLocal(arg - 1, previousLocalType | TOP_IF_LONG_OR_DOUBLE_FLAG);
          }
        }
        break;
      case Opcodes.IASTORE:
      case Opcodes.BASTORE:
      case Opcodes.CASTORE:
      case Opcodes.SASTORE:
      case Opcodes.FASTORE:
      case Opcodes.AASTORE:
        pop(3);
        break;
      case Opcodes.LASTORE:
      case Opcodes.DASTORE:
        pop(4);
        break;
      case Opcodes.POP:
      case Opcodes.IFEQ:
      case Opcodes.IFNE:
      case Opcodes.IFLT:
      case Opcodes.IFGE:
      case Opcodes.IFGT:
      case Opcodes.IFLE:
      case Opcodes.IRETURN:
      case Opcodes.FRETURN:
      case Opcodes.ARETURN:
      case Opcodes.TABLESWITCH:
      case Opcodes.LOOKUPSWITCH:
      case Opcodes.ATHROW:
      case Opcodes.MONITORENTER:
      case Opcodes.MONITOREXIT:
      case Opcodes.IFNULL:
      case Opcodes.IFNONNULL:
        pop(1);
        break;
      case Opcodes.POP2:
      case Opcodes.IF_ICMPEQ:
      case Opcodes.IF_ICMPNE:
      case Opcodes.IF_ICMPLT:
      case Opcodes.IF_ICMPGE:
      case Opcodes.IF_ICMPGT:
      case Opcodes.IF_ICMPLE:
      case Opcodes.IF_ACMPEQ:
      case Opcodes.IF_ACMPNE:
      case Opcodes.LRETURN:
      case Opcodes.DRETURN:
        pop(2);
        break;
      case Opcodes.DUP:
        abstractType1 = pop();
        push(abstractType1);
        push(abstractType1);
        break;
      case Opcodes.DUP_X1:
        abstractType1 = pop();
        abstractType2 = pop();
        push(abstractType1);
        push(abstractType2);
        push(abstractType1);
        break;
      case Opcodes.DUP_X2:
        abstractType1 = pop();
        abstractType2 = pop();
        abstractType3 = pop();
        push(abstractType1);
        push(abstractType3);
        push(abstractType2);
        push(abstractType1);
        break;
      case Opcodes.DUP2:
        abstractType1 = pop();
        abstractType2 = pop();
        push(abstractType2);
        push(abstractType1);
        push(abstractType2);
        push(abstractType1);
        break;
      case Opcodes.DUP2_X1:
        abstractType1 = pop();
        abstractType2 = pop();
        abstractType3 = pop();
        push(abstractType2);
        push(abstractType1);
        push(abstractType3);
        push(abstractType2);
        push(abstractType1);
        break;
      case Opcodes.DUP2_X2:
        abstractType1 = pop();
        abstractType2 = pop();
        abstractType3 = pop();
        abstractType4 = pop();
        push(abstractType2);
        push(abstractType1);
        push(abstractType4);
        push(abstractType3);
        push(abstractType2);
        push(abstractType1);
        break;
      case Opcodes.SWAP:
        abstractType1 = pop();
        abstractType2 = pop();
        push(abstractType1);
        push(abstractType2);
        break;
      case Opcodes.IALOAD:
      case Opcodes.BALOAD:
      case Opcodes.CALOAD:
      case Opcodes.SALOAD:
      case Opcodes.IADD:
      case Opcodes.ISUB:
      case Opcodes.IMUL:
      case Opcodes.IDIV:
      case Opcodes.IREM:
      case Opcodes.IAND:
      case Opcodes.IOR:
      case Opcodes.IXOR:
      case Opcodes.ISHL:
      case Opcodes.ISHR:
      case Opcodes.IUSHR:
      case Opcodes.L2I:
      case Opcodes.D2I:
      case Opcodes.FCMPL:
      case Opcodes.FCMPG:
        pop(2);
        push(INTEGER);
        break;
      case Opcodes.LADD:
      case Opcodes.LSUB:
      case Opcodes.LMUL:
      case Opcodes.LDIV:
      case Opcodes.LREM:
      case Opcodes.LAND:
      case Opcodes.LOR:
      case Opcodes.LXOR:
        pop(4);
        push(LONG);
        push(TOP);
        break;
      case Opcodes.FALOAD:
      case Opcodes.FADD:
      case Opcodes.FSUB:
      case Opcodes.FMUL:
      case Opcodes.FDIV:
      case Opcodes.FREM:
      case Opcodes.L2F:
      case Opcodes.D2F:
        pop(2);
        push(FLOAT);
        break;
      case Opcodes.DADD:
      case Opcodes.DSUB:
      case Opcodes.DMUL:
      case Opcodes.DDIV:
      case Opcodes.DREM:
        pop(4);
        push(DOUBLE);
        push(TOP);
        break;
      case Opcodes.LSHL:
      case Opcodes.LSHR:
      case Opcodes.LUSHR:
        pop(3);
        push(LONG);
        push(TOP);
        break;
      case Opcodes.IINC:
        setLocal(arg, INTEGER);
        break;
      case Opcodes.I2L:
      case Opcodes.F2L:
        pop(1);
        push(LONG);
        push(TOP);
        break;
      case Opcodes.I2F:
        pop(1);
        push(FLOAT);
        break;
      case Opcodes.I2D:
      case Opcodes.F2D:
        pop(1);
        push(DOUBLE);
        push(TOP);
        break;
      case Opcodes.F2I:
      case Opcodes.ARRAYLENGTH:
      case Opcodes.INSTANCEOF:
        pop(1);
        push(INTEGER);
        break;
      case Opcodes.LCMP:
      case Opcodes.DCMPL:
      case Opcodes.DCMPG:
        pop(4);
        push(INTEGER);
        break;
      case Opcodes.JSR:
      case Opcodes.RET:
        throw new IllegalArgumentException("JSR/RET are not supported with computeFrames option");
      case Opcodes.GETSTATIC:
        push(symbolTable, argSymbol.value);
        break;
      case Opcodes.PUTSTATIC:
        pop(argSymbol.value);
        break;
      case Opcodes.GETFIELD:
        pop(1);
        push(symbolTable, argSymbol.value);
        break;
      case Opcodes.PUTFIELD:
        pop(argSymbol.value);
        pop();
        break;
      case Opcodes.INVOKEVIRTUAL:
      case Opcodes.INVOKESPECIAL:
      case Opcodes.INVOKESTATIC:
      case Opcodes.INVOKEINTERFACE:
        pop(argSymbol.value);
        if (opcode != Opcodes.INVOKESTATIC) {
          abstractType1 = pop();
          if (opcode == Opcodes.INVOKESPECIAL && argSymbol.name.charAt(0) == '<') {
            addInitializedType(abstractType1);
          }
        }
        push(symbolTable, argSymbol.value);
        break;
      case Opcodes.INVOKEDYNAMIC:
        pop(argSymbol.value);
        push(symbolTable, argSymbol.value);
        break;
      case Opcodes.NEW:
        push(UNINITIALIZED_KIND | symbolTable.addUninitializedType(argSymbol.value, arg));
        break;
      case Opcodes.NEWARRAY:
        pop();
        switch (arg) {
          case Opcodes.T_BOOLEAN:
            push(ARRAY_OF | BOOLEAN);
            break;
          case Opcodes.T_CHAR:
            push(ARRAY_OF | CHAR);
            break;
          case Opcodes.T_BYTE:
            push(ARRAY_OF | BYTE);
            break;
          case Opcodes.T_SHORT:
            push(ARRAY_OF | SHORT);
            break;
          case Opcodes.T_INT:
            push(ARRAY_OF | INTEGER);
            break;
          case Opcodes.T_FLOAT:
            push(ARRAY_OF | FLOAT);
            break;
          case Opcodes.T_DOUBLE:
            push(ARRAY_OF | DOUBLE);
            break;
          case Opcodes.T_LONG:
            push(ARRAY_OF | LONG);
            break;
          default:
            throw new IllegalArgumentException();
        }
        break;
      case Opcodes.ANEWARRAY:
        String arrayElementType = argSymbol.value;
        pop();
        if (arrayElementType.charAt(0) == '[') {
          push(symbolTable, '[' + arrayElementType);
        } else {
          push(ARRAY_OF | REFERENCE_KIND | symbolTable.addType(arrayElementType));
        }
        break;
      case Opcodes.CHECKCAST:
        String castType = argSymbol.value;
        pop();
        if (castType.charAt(0) == '[') {
          push(symbolTable, castType);
        } else {
          push(REFERENCE_KIND | symbolTable.addType(castType));
        }
        break;
      case Opcodes.MULTIANEWARRAY:
        pop(arg);
        push(symbolTable, argSymbol.value);
        break;
      default:
        throw new IllegalArgumentException();
    }
  }

  // -----------------------------------------------------------------------------------------------
  // Frame merging methods, used in the second step of the stack map frame computation algorithm
  // -----------------------------------------------------------------------------------------------

  Computes the concrete output type corresponding to a given abstract output type.
Params: abstractOutputType – an abstract output type.
numStack – the size of the input stack, used to resolve abstract output types of
    STACK_KIND kind.
Returns: the concrete output type corresponding to 'abstractOutputType'./**
   * Computes the concrete output type corresponding to a given abstract output type.
   *
   * @param abstractOutputType an abstract output type.
   * @param numStack the size of the input stack, used to resolve abstract output types of
   *     STACK_KIND kind.
   * @return the concrete output type corresponding to 'abstractOutputType'.
   */
  private int getConcreteOutputType(final int abstractOutputType, final int numStack) {
    int dim = abstractOutputType & DIM_MASK;
    int kind = abstractOutputType & KIND_MASK;
    if (kind == LOCAL_KIND) {
      // By definition, a LOCAL_KIND type designates the concrete type of a local variable at
      // the beginning of the basic block corresponding to this frame (which is known when
      // this method is called, but was not when the abstract type was computed).
      int concreteOutputType = dim + inputLocals[abstractOutputType & VALUE_MASK];
      if ((abstractOutputType & TOP_IF_LONG_OR_DOUBLE_FLAG) != 0
          && (concreteOutputType == LONG || concreteOutputType == DOUBLE)) {
        concreteOutputType = TOP;
      }
      return concreteOutputType;
    } else if (kind == STACK_KIND) {
      // By definition, a STACK_KIND type designates the concrete type of a local variable at
      // the beginning of the basic block corresponding to this frame (which is known when
      // this method is called, but was not when the abstract type was computed).
      int concreteOutputType = dim + inputStack[numStack - (abstractOutputType & VALUE_MASK)];
      if ((abstractOutputType & TOP_IF_LONG_OR_DOUBLE_FLAG) != 0
          && (concreteOutputType == LONG || concreteOutputType == DOUBLE)) {
        concreteOutputType = TOP;
      }
      return concreteOutputType;
    } else {
      return abstractOutputType;
    }
  }

  Merges the input frame of the given Frame with the input and output frames of this Frame. Returns true if the given frame has been changed by this operation (the input and output frames of this Frame are never changed). 
Params: symbolTable – the type table to use to lookup and store type Symbol.
dstFrame – the Frame whose input frame must be updated. This should be the frame of a successor, in the control flow graph, of the basic block corresponding to this frame.
catchTypeIndex – if 'frame' corresponds to an exception handler basic block, the type
    table index of the caught exception type, otherwise 0.
Returns: true if the input frame of 'frame' has been changed by this operation./**
   * Merges the input frame of the given {@link Frame} with the input and output frames of this
   * {@link Frame}. Returns {@literal true} if the given frame has been changed by this operation
   * (the input and output frames of this {@link Frame} are never changed).
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param dstFrame the {@link Frame} whose input frame must be updated. This should be the frame
   *     of a successor, in the control flow graph, of the basic block corresponding to this frame.
   * @param catchTypeIndex if 'frame' corresponds to an exception handler basic block, the type
   *     table index of the caught exception type, otherwise 0.
   * @return {@literal true} if the input frame of 'frame' has been changed by this operation.
   */
  final boolean merge(
      final SymbolTable symbolTable, final Frame dstFrame, final int catchTypeIndex) {
    boolean frameChanged = false;

    // Compute the concrete types of the local variables at the end of the basic block corresponding
    // to this frame, by resolving its abstract output types, and merge these concrete types with
    // those of the local variables in the input frame of dstFrame.
    int numLocal = inputLocals.length;
    int numStack = inputStack.length;
    if (dstFrame.inputLocals == null) {
      dstFrame.inputLocals = new int[numLocal];
      frameChanged = true;
    }
    for (int i = 0; i < numLocal; ++i) {
      int concreteOutputType;
      if (outputLocals != null && i < outputLocals.length) {
        int abstractOutputType = outputLocals[i];
        if (abstractOutputType == 0) {
          // If the local variable has never been assigned in this basic block, it is equal to its
          // value at the beginning of the block.
          concreteOutputType = inputLocals[i];
        } else {
          concreteOutputType = getConcreteOutputType(abstractOutputType, numStack);
        }
      } else {
        // If the local variable has never been assigned in this basic block, it is equal to its
        // value at the beginning of the block.
        concreteOutputType = inputLocals[i];
      }
      // concreteOutputType might be an uninitialized type from the input locals or from the input
      // stack. However, if a constructor has been called for this class type in the basic block,
      // then this type is no longer uninitialized at the end of basic block.
      if (initializations != null) {
        concreteOutputType = getInitializedType(symbolTable, concreteOutputType);
      }
      frameChanged |= merge(symbolTable, concreteOutputType, dstFrame.inputLocals, i);
    }

    // If dstFrame is an exception handler block, it can be reached from any instruction of the
    // basic block corresponding to this frame, in particular from the first one. Therefore, the
    // input locals of dstFrame should be compatible (i.e. merged) with the input locals of this
    // frame (and the input stack of dstFrame should be compatible, i.e. merged, with a one
    // element stack containing the caught exception type).
    if (catchTypeIndex > 0) {
      for (int i = 0; i < numLocal; ++i) {
        frameChanged |= merge(symbolTable, inputLocals[i], dstFrame.inputLocals, i);
      }
      if (dstFrame.inputStack == null) {
        dstFrame.inputStack = new int[1];
        frameChanged = true;
      }
      frameChanged |= merge(symbolTable, catchTypeIndex, dstFrame.inputStack, 0);
      return frameChanged;
    }

    // Compute the concrete types of the stack operands at the end of the basic block corresponding
    // to this frame, by resolving its abstract output types, and merge these concrete types with
    // those of the stack operands in the input frame of dstFrame.
    int numInputStack = inputStack.length + outputStackStart;
    if (dstFrame.inputStack == null) {
      dstFrame.inputStack = new int[numInputStack + outputStackTop];
      frameChanged = true;
    }
    // First, do this for the stack operands that have not been popped in the basic block
    // corresponding to this frame, and which are therefore equal to their value in the input
    // frame (except for uninitialized types, which may have been initialized).
    for (int i = 0; i < numInputStack; ++i) {
      int concreteOutputType = inputStack[i];
      if (initializations != null) {
        concreteOutputType = getInitializedType(symbolTable, concreteOutputType);
      }
      frameChanged |= merge(symbolTable, concreteOutputType, dstFrame.inputStack, i);
    }
    // Then, do this for the stack operands that have pushed in the basic block (this code is the
    // same as the one above for local variables).
    for (int i = 0; i < outputStackTop; ++i) {
      int abstractOutputType = outputStack[i];
      int concreteOutputType = getConcreteOutputType(abstractOutputType, numStack);
      if (initializations != null) {
        concreteOutputType = getInitializedType(symbolTable, concreteOutputType);
      }
      frameChanged |=
          merge(symbolTable, concreteOutputType, dstFrame.inputStack, numInputStack + i);
    }
    return frameChanged;
  }

  Merges the type at the given index in the given abstract type array with the given type. Returns true if the type array has been modified by this operation. 
Params: symbolTable – the type table to use to lookup and store type Symbol.
sourceType – the abstract type with which the abstract type array element must be merged. This type should be of CONSTANT_KIND, REFERENCE_KIND or UNINITIALIZED_KIND kind, with positive or null array dimensions.
dstTypes – an array of abstract types. These types should be of CONSTANT_KIND, REFERENCE_KIND or UNINITIALIZED_KIND kind, with positive or 
    null array dimensions.
dstIndex – the index of the type that must be merged in dstTypes.
Returns: true if the type array has been modified by this operation./**
   * Merges the type at the given index in the given abstract type array with the given type.
   * Returns {@literal true} if the type array has been modified by this operation.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param sourceType the abstract type with which the abstract type array element must be merged.
   *     This type should be of {@link #CONSTANT_KIND}, {@link #REFERENCE_KIND} or {@link
   *     #UNINITIALIZED_KIND} kind, with positive or {@literal null} array dimensions.
   * @param dstTypes an array of abstract types. These types should be of {@link #CONSTANT_KIND},
   *     {@link #REFERENCE_KIND} or {@link #UNINITIALIZED_KIND} kind, with positive or {@literal
   *     null} array dimensions.
   * @param dstIndex the index of the type that must be merged in dstTypes.
   * @return {@literal true} if the type array has been modified by this operation.
   */
  private static boolean merge(
      final SymbolTable symbolTable,
      final int sourceType,
      final int[] dstTypes,
      final int dstIndex) {
    int dstType = dstTypes[dstIndex];
    if (dstType == sourceType) {
      // If the types are equal, merge(sourceType, dstType) = dstType, so there is no change.
      return false;
    }
    int srcType = sourceType;
    if ((sourceType & ~DIM_MASK) == NULL) {
      if (dstType == NULL) {
        return false;
      }
      srcType = NULL;
    }
    if (dstType == 0) {
      // If dstTypes[dstIndex] has never been assigned, merge(srcType, dstType) = srcType.
      dstTypes[dstIndex] = srcType;
      return true;
    }
    int mergedType;
    if ((dstType & DIM_MASK) != 0 || (dstType & KIND_MASK) == REFERENCE_KIND) {
      // If dstType is a reference type of any array dimension.
      if (srcType == NULL) {
        // If srcType is the NULL type, merge(srcType, dstType) = dstType, so there is no change.
        return false;
      } else if ((srcType & (DIM_MASK | KIND_MASK)) == (dstType & (DIM_MASK | KIND_MASK))) {
        // If srcType has the same array dimension and the same kind as dstType.
        if ((dstType & KIND_MASK) == REFERENCE_KIND) {
          // If srcType and dstType are reference types with the same array dimension,
          // merge(srcType, dstType) = dim(srcType) | common super class of srcType and dstType.
          mergedType =
              (srcType & DIM_MASK)
                  | REFERENCE_KIND
                  | symbolTable.addMergedType(srcType & VALUE_MASK, dstType & VALUE_MASK);
        } else {
          // If srcType and dstType are array types of equal dimension but different element types,
          // merge(srcType, dstType) = dim(srcType) - 1 | java/lang/Object.
          int mergedDim = ELEMENT_OF + (srcType & DIM_MASK);
          mergedType = mergedDim | REFERENCE_KIND | symbolTable.addType("java/lang/Object");
        }
      } else if ((srcType & DIM_MASK) != 0 || (srcType & KIND_MASK) == REFERENCE_KIND) {
        // If srcType is any other reference or array type,
        // merge(srcType, dstType) = min(srcDdim, dstDim) | java/lang/Object
        // where srcDim is the array dimension of srcType, minus 1 if srcType is an array type
        // with a non reference element type (and similarly for dstDim).
        int srcDim = srcType & DIM_MASK;
        if (srcDim != 0 && (srcType & KIND_MASK) != REFERENCE_KIND) {
          srcDim = ELEMENT_OF + srcDim;
        }
        int dstDim = dstType & DIM_MASK;
        if (dstDim != 0 && (dstType & KIND_MASK) != REFERENCE_KIND) {
          dstDim = ELEMENT_OF + dstDim;
        }
        mergedType =
            Math.min(srcDim, dstDim) | REFERENCE_KIND | symbolTable.addType("java/lang/Object");
      } else {
        // If srcType is any other type, merge(srcType, dstType) = TOP.
        mergedType = TOP;
      }
    } else if (dstType == NULL) {
      // If dstType is the NULL type, merge(srcType, dstType) = srcType, or TOP if srcType is not a
      // an array type or a reference type.
      mergedType =
          (srcType & DIM_MASK) != 0 || (srcType & KIND_MASK) == REFERENCE_KIND ? srcType : TOP;
    } else {
      // If dstType is any other type, merge(srcType, dstType) = TOP whatever srcType.
      mergedType = TOP;
    }
    if (mergedType != dstType) {
      dstTypes[dstIndex] = mergedType;
      return true;
    }
    return false;
  }

  // -----------------------------------------------------------------------------------------------
  // Frame output methods, to generate StackMapFrame attributes
  // -----------------------------------------------------------------------------------------------

  Makes the given MethodWriter visit the input frame of this Frame. The visit is done with the MethodWriter.visitFrameStart, MethodWriter.visitAbstractType and MethodWriter.visitFrameEnd methods. 
Params: methodWriter – the MethodWriter that should visit the input frame of this Frame./**
   * Makes the given {@link MethodWriter} visit the input frame of this {@link Frame}. The visit is
   * done with the {@link MethodWriter#visitFrameStart}, {@link MethodWriter#visitAbstractType} and
   * {@link MethodWriter#visitFrameEnd} methods.
   *
   * @param methodWriter the {@link MethodWriter} that should visit the input frame of this {@link
   *     Frame}.
   */
  final void accept(final MethodWriter methodWriter) {
    // Compute the number of locals, ignoring TOP types that are just after a LONG or a DOUBLE, and
    // all trailing TOP types.
    int[] localTypes = inputLocals;
    int numLocal = 0;
    int numTrailingTop = 0;
    int i = 0;
    while (i < localTypes.length) {
      int localType = localTypes[i];
      i += (localType == LONG || localType == DOUBLE) ? 2 : 1;
      if (localType == TOP) {
        numTrailingTop++;
      } else {
        numLocal += numTrailingTop + 1;
        numTrailingTop = 0;
      }
    }
    // Compute the stack size, ignoring TOP types that are just after a LONG or a DOUBLE.
    int[] stackTypes = inputStack;
    int numStack = 0;
    i = 0;
    while (i < stackTypes.length) {
      int stackType = stackTypes[i];
      i += (stackType == LONG || stackType == DOUBLE) ? 2 : 1;
      numStack++;
    }
    // Visit the frame and its content.
    int frameIndex = methodWriter.visitFrameStart(owner.bytecodeOffset, numLocal, numStack);
    i = 0;
    while (numLocal-- > 0) {
      int localType = localTypes[i];
      i += (localType == LONG || localType == DOUBLE) ? 2 : 1;
      methodWriter.visitAbstractType(frameIndex++, localType);
    }
    i = 0;
    while (numStack-- > 0) {
      int stackType = stackTypes[i];
      i += (stackType == LONG || stackType == DOUBLE) ? 2 : 1;
      methodWriter.visitAbstractType(frameIndex++, stackType);
    }
    methodWriter.visitFrameEnd();
  }

  Put the given abstract type in the given ByteVector, using the JVMS verification_type_info
format used in StackMapTable attributes.
Params: symbolTable – the type table to use to lookup and store type Symbol.
abstractType – an abstract type, restricted to CONSTANT_KIND, REFERENCE_KIND or UNINITIALIZED_KIND types.
output – where the abstract type must be put.
See Also: JVMS
   *     4.7.4/**
   * Put the given abstract type in the given ByteVector, using the JVMS verification_type_info
   * format used in StackMapTable attributes.
   *
   * @param symbolTable the type table to use to lookup and store type {@link Symbol}.
   * @param abstractType an abstract type, restricted to {@link Frame#CONSTANT_KIND}, {@link
   *     Frame#REFERENCE_KIND} or {@link Frame#UNINITIALIZED_KIND} types.
   * @param output where the abstract type must be put.
   * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.4">JVMS
   *     4.7.4</a>
   */
  static void putAbstractType(
      final SymbolTable symbolTable, final int abstractType, final ByteVector output) {
    int arrayDimensions = (abstractType & Frame.DIM_MASK) >> DIM_SHIFT;
    if (arrayDimensions == 0) {
      int typeValue = abstractType & VALUE_MASK;
      switch (abstractType & KIND_MASK) {
        case CONSTANT_KIND:
          output.putByte(typeValue);
          break;
        case REFERENCE_KIND:
          output
              .putByte(ITEM_OBJECT)
              .putShort(symbolTable.addConstantClass(symbolTable.getType(typeValue).value).index);
          break;
        case UNINITIALIZED_KIND:
          output.putByte(ITEM_UNINITIALIZED).putShort((int) symbolTable.getType(typeValue).data);
          break;
        default:
          throw new AssertionError();
      }
    } else {
      // Case of an array type, we need to build its descriptor first.
      StringBuilder typeDescriptor = new StringBuilder();
      while (arrayDimensions-- > 0) {
        typeDescriptor.append('[');
      }
      if ((abstractType & KIND_MASK) == REFERENCE_KIND) {
        typeDescriptor
            .append('L')
            .append(symbolTable.getType(abstractType & VALUE_MASK).value)
            .append(';');
      } else {
        switch (abstractType & VALUE_MASK) {
          case Frame.ITEM_ASM_BOOLEAN:
            typeDescriptor.append('Z');
            break;
          case Frame.ITEM_ASM_BYTE:
            typeDescriptor.append('B');
            break;
          case Frame.ITEM_ASM_CHAR:
            typeDescriptor.append('C');
            break;
          case Frame.ITEM_ASM_SHORT:
            typeDescriptor.append('S');
            break;
          case Frame.ITEM_INTEGER:
            typeDescriptor.append('I');
            break;
          case Frame.ITEM_FLOAT:
            typeDescriptor.append('F');
            break;
          case Frame.ITEM_LONG:
            typeDescriptor.append('J');
            break;
          case Frame.ITEM_DOUBLE:
            typeDescriptor.append('D');
            break;
          default:
            throw new AssertionError();
        }
      }
      output
          .putByte(ITEM_OBJECT)
          .putShort(symbolTable.addConstantClass(typeDescriptor.toString()).index);
    }
  }
}
Params:	symbolTable – the type table to use to lookup and store type `Symbol`. internalName – the internal name of a class. This must not be an array type descriptor.
Returns:	the abstract type value corresponding to the given internal name.
Params:	localIndex – the index of the local variable whose value must be returned.
Returns:	the abstract type stored at the given local variable index in the output frame.
Params:	abstractOutputType – an abstract output type. numStack – the size of the input stack, used to resolve abstract output types of STACK_KIND kind.
Returns:	the concrete output type corresponding to 'abstractOutputType'.
Params:	symbolTable – the type table to use to lookup and store type `Symbol`. abstractType – an abstract type, restricted to `CONSTANT_KIND`, `REFERENCE_KIND` or `UNINITIALIZED_KIND` types. output – where the abstract type must be put.
See Also:	JVMS * 4.7.4
/

org.ow2.asm/ asm/ 7.3.1/ org/objectweb/asm/Frame.java
